Stress-induced formation of high-density amorphous carbon thin films

Amorphous carbon films with high ${\mathrm{sp}}^3$ content were deposited by magnetron sputtering and intense argon ion plating. Above a compressive stress of 13 GPa a strong increase of the density of the carbon films is observed. We explain the increase of density by a stress-induced phase transition of ${\mathrm{sp}}^2$ configured carbon to ${\mathrm{sp}}^3$ configured carbon. Preferential sputtering of the ${\mathrm{sp}}^2$ component in the carbon films plays a minor role compared to the ${\mathrm{sp}}^2{\mathrm{\Rightarrow sp}}^3$ transition at high compressive stress formed during the deposition process. Transmission electron microscopy shows evidence of graphitic regions in the magnetron sputtered/Ar plated amorphous carbon thin films. Differences in the microstructure of the tetrahedral amorphous carbon (ta–C) films deposited by filtered arc and mass selected ion beam; and those films deposited using magnetron sputtering combined with intense ion plating can be used to explain the different electronic and optical properties of both kinds of ta–C films.